Sherwood RD-6108 receiver turns on and off randomly.

I don't have a service manual for this receiver but I checked the 6V standby voltage and the 15V line from the standby power supply and they both are at the correct voltage and have low ripple. I've heated and cooled the boards with no change of symptoms. The problem began by the receiver turning on in the middle of the night. Reset the micro but it happened again 2 hours later. Now it clicks off when on from anywhere from 2 seconds to hours. Is there a common fault for this receiver causing these symptoms? Thanks. Chuck

Reply to
Chuck
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Silly suggestion - does a piece of black tape over the IR sensor help at al l? I suggest because I am seeing lots of "smart house" stuff starting to in terfere with some legacy equipment out there. You might also isolate the re mote as some of the touch-pad contacts may be aging and making random conta ct. That is to get past the obvious.

Otherwise, I would trace out the on/off circuit and look for a bad capacito r on in that lot. This unit is approaching 18 years old, or so, about the t ime these tiny little electrolytics start to fail.

Best of luck with it!

Reply to
peterwieck33

Check for current leakage in the areas around the on/off switch.

Some decades ago I had a Macintosh II which had a habit of turning itself on without human intervention - usually in the morning.

I eventually traced the problem to the keyboard. The Mac II uses a "soft" power switching setup, where the keyboard power switch pulls one of the ADB-cable lines down to ground. This sense line has a very high source impedance, and it didn't take much current leakage to ground to false-trigger it.

The Mac II was in a spare bedroom that got quite cold at night during the winter (the place we were renting had a lousy heating system and no insulation). In the morning, my wife would take a shower, humid air would flood the back of the house, some moisture would condense inside the cold keyboard case, and a few microamps of current would leak across the switch contacts. BONG!

I cleaned the keyboard's PC board in the area of the switch with some alcohol, coated it with something insulating (I think I used a thin film of my wife's acrylic nail polish) and the problem went away.

So, I'd suggest inspecting the power switch and the PC board around it. Possibly some old flux, or the dreaded "yellow glue" on the board has become conductive with age. Clean it all up thoroughly (careful scraping, flux-remover spray, etc.), dry well, and apply a conformal insulation coating of some sort, and see if that resolves the problem.

Looking at the manual for the RD-6106 (which may be similar) - this receiver does seem to have a "soft" power switching system, where the main AC voltage can be controlled by both a "hard" switch, and by a relay system driven from the control logic. The control logic then looks at a "standby" pushbutton... this is a low-level contact closure and seems to be tied in with the main keyboard scanning logic. So, a contaminated "standby" PC board / assembly might be at fault.

Reply to
Dave Platt

Thank you for your input. I had removed the conductive glue from the boards with no improvement. I've seen the leaky tact switch faults on tvs, but I didn't think of it in this case. Will disconnect it and see if the receiver stays on.

Reply to
Chuck

Yes, I covered the IR window but I didn't disconnect the IR receiver which have caused weird tv symptoms. Thank you for your suggestions.

Reply to
Chuck

David, As you surmised, the problem was the power tact switch. I didn't check it because I heard a weird distortion while playing a cd the night before. So I thought the problem was a voltage inbalance causing the protection circuit to engage. The last unit I repaired was a dehumidifier where every tact switch was open so luckily I had the switch in stock. Years ago a high end Technics cassette deck came into the shop. Every tact switch was open so I asked the customer what environment the unit was used in. It was used in a room where metal was etched. The fumes ate away the tact switches' internals. Thanks for guiding me in the right direction.

Reply to
Chuck H.

Even though I know better, I have screwed diagnosis many times by thinking I knew what the problem might be and going down the wrong path. It's almost irresistible sometimes.

Reply to
Tim R

You bet. I spent 47 years repairing consumer , pro audio, television studio, video conferencing, and server equipment. Though retired, I shouldn't have slipped this much.

Reply to
Chuck

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